The allergen-specific IgE antibody to total serum IgE ratio is a key variable being investigated in relation to allergic symptom induction in this Program Project. The Diagnostic Core will conduct two main activities. In Aims 1 and 2, the Diagnostic Core will provide a service function in which analytical measurements will be performed on serum, cells, tissues, and lavage fluids collected on subjects in the project using validated assays. In Aims 3 and 4, the Diagnostic Core will investigate several hypotheses fundamental to improving the analytical sensitivity of allergen-specific IgE assays and validating the accuracy of the total and "free" (non-Omalizumab bound) total and allergen-specific IgE assays. More specifically, in Aim 1, the Diagnostic Core will provide state-of- the-art serologic, immunohistology, in situ hybridization, mediator and cytokine, nasal lavage chemistries and aeroallergen testing on specimens collected during recruitment and the longitudinal monitoring phases of the studies. Serologic testing (total and allergen-specific IgE, tryptase), nasal lavage chemistries, immunohistology, in situ hybridization, aeroallergen (Pel d 1) and cat extract validation will be performed in or under the auspices of the CLIA-88 certified Johns Hopkins Dermatology Allergy and Clinical Immunology (DACI) Reference Laboratory. In Aim 2, The Diagnostic Core Group will quantify "free" (non-Omalizumab bound) total IgE measurements in serum of subjects who have received Omalizumab to reduce free IgE levels, using our newly developed immunoenzymetric assay. A free allergen-specific IgE antibody assay will also be developed and configured on the ImmunoCAP platform to permit free specific to total IgE ratios to be computed. Aim 3 will investigate the hypothesis that 1 nanogram of allergen-specific IgE antibody as measured in a 3rd generation FDA-cleared assay equals 1 nanogram of total serum IgE. Verification of this quantitative relationship is critical to the accurate measurement of the specific to total IgE ratio. Aim 4 will investigate the hypothesis that the allergen-specific to total serum IgE ratio in allergic subjects before treatment with an IgE lowering drug (Omalizumab) remains constant for months during and following treatment, despite a expected many fold increase in total serum IgE. It is anticipated that Aims 3 and 4 will be completed within year 1 of the program so that free specific to total IgE ratio measurements will be available to investigations conducted in the 3 projects in this program.